An optical information processor reads information from a storage medium or writes information on a storage medium by irradiating it with light radiated from a light source. The processor includes: the light source for radiating the light; a condensing element for converging the light, radiated from the light source, toward the storage medium; and a detector for detecting a portion of the light radiated from the light source. Supposing that in a far-field pattern of the light radiated from the light source, an aperture area A is defined by a portion of the light entering the condensing element and a photosensitive area b is defined by another part of the light entering the detector and that the light has the narrower angle of radiation in an x direction and the wider angle of radiation in a y direction, respectively, the center of the photosensitive area b in the x direction is offset with respect to that of the far-field pattern in the x direction.
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1. An optical information processor for at least one of reading information from a storage medium and writing information on a storage medium by irradiating the storage medium with light that has been radiated from a light source, the optical information processor comprising:
the light source for radiating the light;
a condensing element for converging the light, radiated from the light source, toward the storage medium; and
a detector for detecting a portion of the light that has been radiated from the light source,
wherein in a far-field pattern of the light radiated from the light source, an aperture area A is defined by a part of the light entering the condensing element and a photosensitive area b is defined by another part of the light entering the detector and the light has the narrower angle of radiation in an x direction and the wider angle of radiation in a y direction, respectively, and the center of the photosensitive area b in the x direction is offset with respect to that of the far-field pattern in the x direction.
7. An optical information processor for at least one of reading information from a storage medium and writing information on a storage medium by irradiating the storage medium with light beams that have been radiated from a plurality of light sources, the optical information processor comprising:
first and second light sources;
a condensing element for converging the light beams, radiated from the first and second light sources, toward the storage medium; and
a detector for detecting respective portions of the light beams that have been radiated from the first and second light sources,
wherein in a first far-field pattern of the light beam radiated from the first light source, an aperture area A1 is defined by a portion of the light beam entering the condensing element and a photosensitive area b1 is defined by another part of the light beam entering the detector and the light beam has the narrower angle of radiation in an x direction and the wider angle of radiation in a y direction, respectively, and the center of the photosensitive area b1 in the x direction is offset with respect to that of the first far-field pattern in the x direction, and
wherein in a second far-field pattern of the light beam radiated from the second light source, an aperture area A2 is defined by a portion of the light beam entering the condensing element and a photosensitive area b2 is defined by another part of the light beam entering the detector and the light beam has the narrower angle of radiation in the x direction and the wider angle of radiation in the y direction, respectively, and the center of the photosensitive area b2 in the x direction is offset with respect to that of the second far-field pattern in the x direction.
2. The optical information processor of
rAx>rBx and
dAx<dBx.
3. The optical information processor of
dAx<0.25 rAx and
0.25 rAx<dBx<0.55 rAx.
4. The optical information processor of
dBy>dAy.
5. The optical information processor of
dBy>rAy.
6. The optical information processor of
wherein optical axes defined from the light sources to the condensing element are aligned with each other at least partially.
8. The optical information processor of
wherein the aperture area A2 has a width of 2 rA2x in the x direction, the photosensitive area b2 has a width of 2 rB2x in the x direction, a distance from the center of the aperture area A2 in the x direction to the center of light intensity distribution of the second far-field pattern in the x direction is dA2x, and a distance from the center of the photosensitive area b2 in the x direction to the center of the light intensity distribution of the second far-field pattern in the x direction is dB2x, respectively,
rA1x, rB1x, dA1x, dB1x, rA2x, rB2x, dA2x and dB2x satisfy
rA1x>rB1x,
rA2x>rB2x,
(rA1x/rB1x)>(rA2x/rB2x) and
(dB1x/rB1x)>(dB2x/rB2x).
9. The optical information processor of
dA1x<0.25 rA1x and
0.25 rA1x<dB1x<0.55 rA1x.
10. The optical information processor of
dB1y>dA1y.
11. The optical information processor of
dB1y>rA1y.
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1. Field of the Invention
The present invention relates to an optical information processor for optically reading information from a storage medium or writing information on a storage medium.
2. Description of the Related Art
Recently, various types of optical information processors for reading and writing information optically have become more and more popular. Among other things, optical disk drives for reading and writing data, representing various types of information including video, image and audio, from/on a disk storage medium such as a Compact Disc (CD), a Mini Disk (MD), a Digital Versatile Disc (DVD) and a Blu-ray Disc (BD), have become particularly popular among consumers.
In each of these drives, a semiconductor laser is usually used as a light source to perform read and write operations. The light that has been radiated from the semiconductor laser is converged by a lens or any other optical element on a storage medium. In writing data on the storage medium, the optical power of the semiconductor laser is set relatively high, thereby increasing the intensity of the light that makes a beam spot on the storage medium and changing a physical property (such as the reflectance or magnetic property) of the storage medium. In this manner, the data is written as marks or pits on the storage medium. In reading data from the storage medium, on the other hand, the optical power of the semiconductor laser is set lower than in the write operation, thereby sensing a variation in the physical property (such as the reflectance or magnetic property) of the storage medium at the marks or pits and reading the data from the storage medium.
Thus, such a drive needs to change the optical power of its light source in a broad range from the low power to the high power. Also, the best light intensity of the beam spot to write data with good stability changes from one drive to another according to the rate of scanning done on the storage medium or the type of the given storage medium. For these reasons, in performing a write operation, the optical power of the light source needs to be controlled so as to keep the best writing conditions always.
Meanwhile, there are increasing demands for high-speed data writing these days. To write data on the same type of storage medium faster, a technique of increasing the rate of scanning the storage medium is usually adopted. However, as the scanning rate is increased, the energy of the radiated light applied to a unit area of the storage medium decreases. That is why to ensure the minimum required light intensity for writing, the optical power of the light source must be further increased.
On the other hand, various techniques of increasing the storage densities have also been researched thoroughly nowadays. As a result, the physical dimensions of marks or pits to be left on a storage medium have become smaller and smaller. To make (or record) those small marks on a storage medium just as intended, not only the amount of time in which the storage medium is irradiated with the light but also the intensity of the radiated light need to be controlled with high precision.
Thus, in order to control the optical power of the light source highly precisely in a broad range, an optical disk drive detects the intensity of the light emitted from the light source and controls the optical power of the light source based on the result of the detection. More specifically, the optical power of the light source is monitored in real time by getting a portion of the emission of the light source detected by a detector, thereby controlling the optical output of the light source (see Japanese Patent Publication No. 2907759, for example).
This conventional technique will be outlined with reference to
Recently, a semiconductor laser called a “real refractive index guided laser”, of which the operating current is reduced for the purpose of increasing its optical power and improving its performance at elevated temperatures, has been used actually (see Matsushita Technical Journal Vol. 45, No. 6 (December 1999), for example). This semiconductor laser is characterized in that the angle of radiation of its emission in the horizontal direction generally changes according to its optical power.
If a real refractive index guided laser having such a characteristic is used as the light source of an optical disk drive, the ratio of the intensity of the light that enters the optical power monitoring detector (which will be identified herein by Pm) to that of the light that enters the storage medium through the condenser lens (which will be identified herein by Po) changes according to the optical power. As a result, the linearity of the Pm/Po ratio cannot be maintained and it is difficult to control the optical power precisely. As shown in
This is because the aperture area 232 (Area A) of the condenser lens and the photosensitive area 233 (Area B) of the optical power monitoring detector have mutually different sizes and shapes as shown in
That is to say, if the coupling efficiencies when the semiconductor laser has an optical power P1 are represented by ηA1 and ηB1 and the coupling efficiencies when the semiconductor laser has an optical power P2 are represented by ηA2 and ηB2, then
is satisfied.
As a result, the linearity of the Pm/Po ratio (=ηB/ηA) is lost. In that case, the optical power of the semiconductor laser cannot be controlled precisely anymore. That is to say, the optical power of the semiconductor laser deviates from its target value.
In order to overcome the problems described above, an object of the present invention is to provide an optical information processor that can monitor the optical power accurately.
An optical information processor according to a preferred embodiment of the present invention is designed to read information from a storage medium or writes information on a storage medium by irradiating the storage medium with light that has been radiated from a light source. The optical information processor preferably includes: the light source for radiating the light; a condensing element for converging the light, radiated from the light source, toward the storage medium; and a detector for detecting a portion of the light that has been radiated from the light source. Supposing that in a far-field pattern of the light radiated from the light source, an aperture area A is defined by a part of the light entering the condensing element and a photosensitive area B is defined by another part of the light entering the detector and that the light has the narrower angle of radiation in an x direction and the wider angle of radiation in a y direction, respectively, the center of the photosensitive area B in the x direction is offset with respect to that of the far-field pattern in the x direction.
In one preferred embodiment of the present invention, supposing the aperture area A has a width of 2 rAx in the x direction, the photosensitive area B has a width of 2 rBx in the x direction, a distance from the center of the aperture area A in the x direction to the center of light intensity distribution of the far-field pattern in the x direction is dAx, and a distance from the center of the photosensitive area B in the x direction to the center of the light intensity distribution of the far-field pattern in the x direction is dBx, respectively, rAx, rBx, dAx and dBx preferably satisfy rAx>rBx and dAx<dBx.
In this particular preferred embodiment, rAx, rBx, dAx and dBx satisfy dAx<0.25 rAx and 0.25 rAx<dBx<0.55 rAx.
In an alternative preferred embodiment, supposing a distance from the center of the aperture area A in the y direction to the center of the light intensity distribution of the far-field pattern in the y direction is dAy and a distance from the center of the photosensitive area B in the y direction to the center of the light intensity distribution of the far-field pattern in the y direction is dBy, respectively, dAy and dBy preferably satisfy dBy>dAy.
In a specific preferred embodiment, supposing the aperture area A has a width of 2 rAy in the y direction, dBy and rAy preferably satisfy dBy>rAy.
In still another preferred embodiment, the optical information processor may further include at least one more light source and optical axes defined from the light sources to the condensing element may be aligned with each other at least partially.
An optical information processor according to another preferred embodiment of the present invention is designed to read information from a storage medium or write information on a storage medium by irradiating the storage medium with light beams that have been radiated from a plurality of light sources. The optical information processor preferably includes: first and second light sources; a condensing element for converging the light beams, radiated from the first and second light sources, toward the storage medium; and a detector for detecting respective portions of the light beams that have been radiated from the first and second light sources. Supposing that in a first far-field pattern of the light beam radiated from the first light source, an aperture area A1 is defined by a portion of the light beam entering the condensing element and a photosensitive area B1 is defined by another part of the light beam entering the detector and that the light beam has the narrower angle of radiation in an x direction and the wider angle of radiation in a y direction, respectively, the center of the photosensitive area B1 in the x direction is offset with respect to that of the first far-field pattern in the x direction. Supposing that in a second far-field pattern of the light beam radiated from the second light source, an aperture area A2 is defined by a portion of the light beam entering the condensing element and a photosensitive area B2 is defined by another part of the light beam entering the detector and that the light beam has the narrower angle of radiation in the x direction and the wider angle of radiation in the y direction, respectively, the center of the photosensitive area B2 in the x direction is offset with respect to that of the second far-field pattern in the x direction.
In one preferred embodiment of the present invention, supposing the aperture area A1 has a width of 2 rA1x in the x direction, the photosensitive area A1 has a width of 2 rB1x in the x direction, a distance from the center of the aperture area A1 in the x direction to the center of light intensity distribution of the first far-field pattern in the x direction is dA1x, and a distance from the center of the photosensitive area B1 in the x direction to the center of the light intensity distribution of the first far-field pattern in the x direction is dB1x, respectively, and supposing the aperture area A2 has a width of 2 rA2x in the x direction, the photosensitive area B1 has a width of 2 rB2x in the x direction, a distance from the center of the aperture area A2 in the x direction to the center of light intensity distribution of the second far-field pattern in the x direction is dA2x, and a distance from the center of the photosensitive area B2 in the x direction to the center of the light intensity distribution of the second far-field pattern in the x direction is dB2x, respectively, rA1x, rB1x, dA1x, dB1x, rA2x, rB2x, x and dB2x satisfy rA1x>rB1x, rA2x>rB2x, (rA1x/rB1x)>(rA2x/rB2x) and (dB1x/rB1x)>(dB2x/rB2x).
In this particular preferred embodiment, rA1x, rB1x, dA1x and dB1x preferably satisfy dA1x<0.25 rA1x and 0.25 rA1x<dB1x<0.55 rA1x.
In another preferred embodiment, supposing a distance from the center of the aperture area A1 in the y direction to the center of the light intensity distribution of the first far-field pattern in the y direction is dA1y and a distance from the center of the photosensitive area B1 in the y direction to the center of the light intensity distribution of the first far-field pattern in the y direction is dB1y, respectively, dA1y and dB1y preferably satisfy dB1y>dA1y.
In a specific preferred embodiment, supposing the aperture area A1 has a width of 2 rA1y in the y direction, dB1y and rA1y preferably satisfy dB1y>rA1y.
According to the present invention, in the far-field pattern of light that has been radiated from a light source, the center of the photosensitive area of a detector is offset with respect to that of the far-field pattern in the direction in which the light has the narrower angle of radiation. That is why even if the angle of radiation of the light emitted from the light source changes according to the optical power, the ratio of the intensity of the light entering the detector to that of the light entering the storage medium by way of the condenser lens varies to a much lesser degree with the optical power. Therefore, even if the optical power changes in a broad range, the output of the light source can be controlled with high precision. As a result, an optical information processor that can read and write information from/on a high-density storage medium at high speeds is realized.
Other features, elements, processes, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.
Hereinafter, an optical disk drive for at least one of reading from a disk storage medium and writing on a disk storage medium data, representing various types of information such as video, image and audio will be described as an exemplary optical information processor according to a preferred embodiment of the present invention. However, the present invention can also be used effectively in any other type of optical information processor as long as the processor can read information from a storage medium or write information on a storage medium by irradiating the storage medium with light that has been radiated from a light source. For example, the present invention is also applicable for use in holographic memory apparatuses, semiconductor exposure apparatuses, laser printers, etc.
As shown in
The rotational drive section 518 preferably includes a turntable, on which an optical disk 8 is mounted as an information storage medium, and rotates and drives the optical disk 8 mounted on the turntable. As will be described later, the optical pickup 510 preferably includes a condenser lens that adjusts the converging state of the light entering the data storage side of the disk, and converges the light toward the data storage side of the optical disk 8, thereby reading data from the data storage side or writing data on the data storage side using the converged light.
On receiving the light that has been converged toward, and reflected from, the data storage side, the control system 514 generates a control signal for controlling the rotation of the optical disk 8 and a control signal for controlling the converging state and beam spot of the light to be focused on the data storage side of the optical disk 8. In response to these control signals, the drivers 520 and 522 drive not only the rotational drive section 518 and traverse drive section 516 but also the condensing element drive section (not shown) of the optical pickup 510. The data processing system 512 reads the data from the data storage side based on the reflected light.
The optical system shown in
As shown in
As used herein, the “far-field pattern” means the distribution of the light that has gone out of the semiconductor laser 1 as a light source as observed sufficiently far away from the light source. Suppose the distribution of the outgoing light is observed on a plane P1 that is L mm away from the emission plane of the semiconductor laser 1 as shown in
As shown in
If the aperture area 112 has a width of 2 rAx in the x direction and the photosensitive area 113 has a width of 2 rBx in the x direction as shown in
Hereinafter, it will be described by way of specific examples how dBx changes with Po, Pm and the Pm/Po ratio when the angle of radiation of the emission of the semiconductor laser 1 changes in the x direction. Suppose the optical system is arranged as shown in
As shown in
The present inventors looked for dominating parameters that would be useful to reduce the variation in Pm/Po ratio with Δθx. First, the present inventors measured the effects of dBx in a situation where the semiconductor laser 1 was supposed to have an angle of radiation θx (Lo) of 8 degrees in its low output mode and an angle of radiation θx (Hi) of 10 degrees in its high output mode, respectively. Also, dBx was supposed to be zero and the other parameters were supposed to be the same as in the example described above. The results are shown in
On the other hand, if dBx=0.87 mm, the dependences of Po and Pm on Δθx are represented by the curves 41-b and 42-b, respectively, as shown in
Next, the present inventors measured the effects of dBx in a situation where the semiconductor laser 1 was supposed to have an angle of radiation θx (Lo) of 10 degrees in its low output mode and an angle of radiation θx (Hi) of 12 degrees in its high output mode. Also, dBx was supposed to be zero and the other parameters were supposed to be the same as in the examples described above. The results are shown in
In
On the other hand, if dBx=0.87 mm, the dependences of Po and Pm on Δθx are represented by the curves 51-b and 52-b, respectively, as shown in
A semiconductor laser for use as a light source for writing data on a CD, an MD, a DVD, a BD or any other storage medium has an angle of radiation θx (Lo) of 6 to 8 degrees when its output is relatively low, and is normally used so as to have a difference Δθx of about 2 degrees in angle of radiation between its low and high output modes. Accordingly, as already described with reference to
Next, it will be described how these effects manifest themselves when the focal length fc of the collimator lens 3 is changed. The results obtained when fc=15 mm are shown in
If dBx=0, the dependences of Po and Pm on Δθx are represented by the curves 61-a and 62-a, respectively, as shown in
On the other hand, if dBx=0.87 mm, the dependences of Po and Pm on Δθx are represented by the curves 61-b and 62-b, respectively, as shown in
On the other hand, if dBx=0.87 mm, the dependences of Po and Pm on Δθx are represented by the curves 71-b and 72-b, respectively, as shown in
A variation in the focal length of the collimator lens is equivalent to a variation in the rim intensity of the light entering the condenser lens 7. As used herein, the “rim intensity” means the intensity of the light entering the rim (i.e., the outer edge) of the aperture area 112 of the condenser lens 7 and is expressed in percentages when the highest intensity of the light entering the aperture area 112 of the condenser lens 7 is 100%. If the focal length fc of the collimator lens changes from 15 mm into 25 mm, then the rim intensity of the light entering the condenser lens 7 in the horizontal direction changes from about 8% into about 56%. This range almost covers the entire range of possible rim intensities that may be adopted as a condition for designing an optical system in an optical disk drive for writing data on a CD, an MD, a DVD, a BD or any other storage medium in view of how much the beam spot, made by the condenser lens, has been converged and how efficiently the light emitted from the light source can be used. Accordingly, as long as a normal rim intensity condition is adopted, by offsetting the center of the photosensitive area of the detector with respect to that of the light intensity distribution of the far-field pattern in the direction in which the angle of radiation changes most significantly, the effects of the variation in the angle of radiation can be minimized and the optical power of the light source can be monitored accurately irrespective of the rim intensity (or the focal length of the collimator lens).
Next, it will be described what effects the dimensions of the photosensitive area of the detector 5 will have.
In
On the other hand, if dBx=0.87 mm, the dependences of Po and Pm on Δθx are represented by the curves 81-b and 82-b, respectively, as shown in
Even when the photosensitive area had a radius rB of 0.45 mm, almost the same results were obtained. Specifically, if dBx=0, the dependences of Po and Pm on Δθx are represented by the curves 91-a and 92-a, respectively, as shown in
On the other hand, if dBx=0.87 mm, the dependences of Po and Pm on Δθx are represented by the curves 91-b and 92-b, respectively, as shown in
An optical disk drive for writing data on a CD, an MD, a DVD, a BD or any other storage medium usually monitors the optical power by using a detector that has a photosensitive area with a diameter φ of about 0.5 mm to about 0.9 mm. Accordingly, in such a normal optical disk drive, by offsetting the center of the photosensitive area of the detector by about 0.87 mm with respect to that of the light intensity distribution of the far-field pattern in the direction in which the angle of radiation changes most significantly, the effects of the variation in the angle of radiation can be minimized and the optical power of the light source can be monitored accurately irrespective of the actual dimensions of the photosensitive area of the detector.
Next, it will be described what effects the dimensions of the aperture area of the condenser lens 7 will have. In the following example, the photosensitive area of the detector was supposed to have a radius rB of 0.35 mm.
In
On the other hand, if dBx=0.87 mm, the dependences of Po and Pm on Δθx are represented by the curves 101-b and 102-b, respectively, as shown in
On these conditions, dBk that minimizes the variation in Pm/Po ratio is 0.46 mm. As represented by the curves 101-c and 102-c in
Next,
On the other hand, if dBx=0.87 mm, the dependences of Po and Pm on Δθx are represented by the curves 111-b and 112-b, respectively, as shown in
On these conditions, dBk that minimizes the variation in Pm/Po ratio is 1.13 mm. As represented by the curves 111-c and 112-c in
By analyzing these results, correlation can be found between the radius rA of the aperture area of the condenser lens and the distance dBx from the center of the light intensity distribution of the far-field pattern to that of the photosensitive area of the detector.
In actually designing a drive, however, the best dBx, derived from the dBx/rA ratio, sometimes cannot be adopted because the photodetector sensitivity of the optical power monitoring detector needs to be matched to the intensity of the incoming light and because of various design constraints on the dimensions of the drive, layout rules, and so on. Hereinafter, the range of dBx that can still reduce the variation in Pm/Po ratio with Δθx even in such situations will be defined.
Under the following conditions, if the center of the aperture area of the condenser lens agrees with that of the photosensitive area of the detector (i.e., when dBx=0), then Po and Pm have the Δθx dependences represented by the curves 131-a and 132-a, respectively, as shown in
On these conditions, dBx that could reduce the variation in Pm/Po ratio to ±6% or less was in the range of 0.5 to 1.1.
In the preferred embodiment described above, the center of the aperture area of the condenser lens agrees with that of the light intensity distribution of the far-field pattern of the light radiated from the light source. However, these two centers do not have to agree with each other. More specifically, the center of the aperture area of the condenser lens may have an offset, which should be smaller than the offset dBx of the center of the photosensitive area of the detector in the x direction, with respect to that of the light intensity distribution of the far-field pattern. This is because the change in Po is little affected by a location of the center of the aperture area due to the large aperture area and low rim intensity thereof. For example, as shown by the curve 31-a, if dAx=0 and the radiation θx changes from 8 deg to 10 deg, the Po decreases by 12%. On the other hand, if dAx=0.25rAx under the same condition, the Po decreases by 11%. In this way, the change in Po is little dependent on dAx. Accordingly, supposing the distance from the center of the aperture area of the condenser lens to that of the light intensity distribution of the far-field pattern in the x direction is dAx, the effects of the present invention described above are achieved as long as dAx<0.25 rAx is satisfied.
Also, in the preferred embodiment described above, the aperture area of the condenser lens and the photosensitive area of the detector have circular shapes. Alternatively, these areas may have a rectangular, polygonal or any other suitable shape as described above. Even so, the effects of the present invention are achieved if the aperture and photosensitive areas have widths of 2 rAx and 2 rBx, respectively, in the x direction and if rAx and rBx satisfy the conditions described above.
Also, in a real refractive index guided semiconductor laser, the angle of radiation normally changes with the optical power in the x direction but does not change in the y direction. That is why the center of the photosensitive area of the detector 5 may be offset in the y direction as long as the conditions described above are satisfied. As shown in
However, if the optical system is designed such that the detector 5 detects a portion of the light is going to enter the condenser lens 7 as shown in
As also described above, the center of the aperture area 112 does not have to agree with the center 111C of the far-field pattern 111 in the y direction, either. Instead, the center of the aperture area 112 may have an offset, which should be smaller than the offset of the center of the photosensitive area 113 in the y direction, with respect to the center 111C of the far-field pattern 111. That is to say, supposing the distance from the center of the aperture area of the condenser lens to that of the light intensity distribution of the far-field pattern in the y direction is identified by dAy, dBy>dAy needs to be satisfied.
Furthermore, in the preferred embodiment described above, the optical system is designed such that the detector 5 detects a portion of the light is going to enter the condenser lens 7. However, the detector may also be arranged outside of the optical path of the light that is going to enter the condenser lens 7. For example, a detector 5′ may be arranged on the collimator lens 3 outside of the optical path of the light 2 that is going to enter the condenser lens 7 as shown in
As has been described in detail, according to the present invention, the center of the photosensitive area of a detector offsets with respect to that of the far-field pattern of the light that has been radiated from a light source in the direction in which the light has the narrower angle of radiation. Accordingly, even if the angle of radiation of the light emitted from the light source changes with the optical power, the variation in the Pm/Po ratio (i.e., the ratio of the intensity Pm of the light entering the detector to the intensity Po of the light entering the storage medium by way of a condensing element) with the optical power can be reduced. Particularly, by setting the magnitude of the offset within the range defined above, the variation in Pm/Po ratio with the optical power can be minimized with various constraints on the drive satisfied. To achieve these effects, just the detector needs to be arranged within a predetermined range and there is no need to provide any additional component for the conventional drive. Therefore, even if the optical power varies in a broad range, the output of the light source can be controlled highly precisely using a simple configuration. Consequently, an optical information processor that can read or write information from a high-density storage medium at high speeds is realized.
As in the first preferred embodiment described above, the optical information processor of this second preferred embodiment is also implemented as an optical disk drive. But the optical disk drive of this preferred embodiment includes two semiconductor lasers 1 and 13 that radiate laser beams with mutually different wavelengths. The two semiconductor lasers 1 and 13 are not usually driven simultaneously but one of them is selectively driven according to the type of the given storage medium. If the optical information processor is implemented as an optical disk drive, the semiconductor lasers 1 and 13 may be two of semiconductor lasers for emitting beams with wavelengths of 780 nm, 650 nm and 400 nm for CDs, DVDs, and BDs.
The light 2 emitted from the semiconductor laser 1 as a first light source is transmitted through a beam splitter 15 and transformed by the collimator lens 3 into a parallel beam, only a part of which is transmitted through the reflective mirror 4 and incident onto the optical power monitoring detector 5. The output of the detector 5 is supplied to the laser controller 6, which controls the output of the semiconductor laser 1 based on the output of the detector 5. On the other hand, another part of the light 2 is reflected by the reflective mirror 4, transmitted through the condenser lens 7 and then converged toward the storage medium 8. The light that has been reflected from the data storage layer of the storage medium 8 follows the same path in the opposite direction, and is diffracted by the detecting diffraction element 9, transmitted through the collimator lens 3, and then incident onto the signal detectors 10 and 11, which are arranged near the semiconductor laser 1. The signals generated responsive to the light that has entered the detectors 10 and 11 are then input to the control system 514 and data processing system 512 as already described for the first preferred embodiment.
Meanwhile, the light 14 emitted from the semiconductor laser 13 as a second light source is reflected by the beam splitter 15 and transformed by the collimator lens 3 into a parallel beam, only a part of which is transmitted through the reflective mirror 4 and incident onto the optical power monitoring detector 5. The output of the detector 5 is supplied to the laser controller 6, which controls the output of the semiconductor laser 13 based on the output of the detector 5. On the other hand, another part of the light 14 is reflected by the reflective mirror 4, transmitted through the condenser lens 7 and then converged toward the storage medium 8. The light that has been reflected from the data storage layer of the storage medium 8 follows the same path in the opposite direction, and is diffracted by the detecting diffraction element 9, transmitted through the collimator lens 3, and then incident onto signal detectors 17 and 18, which are arranged near the semiconductor laser 13. The signals generated responsive to the light that has entered the detectors 17 and 18 are then input to the control system 514 and data processing system 512. As shown in
Supposing the aperture area 112 has a width of 2 rAx in the x direction, the photosensitive area 113 has a width of 2 rBx in the x direction, and the distance from the center of the photosensitive area 113 to the center 111C of the far-field pattern 111 in the x direction is dBx, rAx and rBx satisfy the inequality rAx>rBx as in the first preferred embodiment described above. Also, dBx and rA satisfy 0.25<dBx/rA<0.55.
Also, supposing the optical powers of the semiconductor lasers 1 and 13 are identified by Po1 and Po2 and the intensities of the laser beams that have been emitted from these lasers and then have entered the detector 5 are identified by Pm1 and Pm2, respectively, the variations in Pm1/Po1 and Pm2/Po2 ratios can be minimized as in the first preferred embodiment even if the angle of radiation varies with the optical power.
Furthermore, the center of the photosensitive area of the detector 5 may be offset arbitrarily in the y direction. Thus, the variations in Pm1/Po1 and Pm2/Po2 ratios can be reduced by offsetting the center of the photosensitive area in the x direction as described above and the intensity of the light entering the detector can be adjusted by offsetting the center of the photosensitive area in the y direction. Optionally, the photosensitive area may also be arranged outside of the area of the reflective mirror as described above.
In the preferred embodiment described above, the detector is arranged to detect the light that has been transmitted through the reflective mirror 4. However, the detector may be arranged at a different position. For example, the beam splitter 15 may transmit the majority of (e.g., 95% of) the outgoing light of the semiconductor laser 1 and guide it to the collimator lens 3 and may reflect the rest (e.g., about 5%) and guide it to the detector 5 as shown in
As in the second preferred embodiment described above, the optical information processor of this preferred embodiment is also implemented as an optical disk drive including two semiconductor lasers 1 and 13 that radiate laser beams with mutually different wavelengths. However, the semiconductor lasers 1 and 13 of this preferred embodiment are arranged differently from the counterparts of the second preferred embodiment. Specifically, the semiconductor lasers 1 and 13 of this preferred embodiment are arranged adjacent to each other.
As shown in
As shown in
The semiconductor lasers 1 and 13 are arranged in the same package so as to be have a gap Δ between them in the x direction. Also, the semiconductor laser 1 is arranged such that its emission point is located approximately on the optical axis of the optical system. Meanwhile, the semiconductor laser 13 is arranged such that its emission point is offset with respect to the optical axis of the optical system in the x direction. Consequently, the center of the far-field pattern of the light that has been emitted from the semiconductor laser 1 and then incident on the condenser lens 7 substantially agrees with the optical axis of the optical system in the x direction. On the other hand, the center of the far-field pattern of the light that has been emitted from the semiconductor laser 13 and then incident on the condenser lens 7 has an offset with respect to the optical axis of the optical system in the x direction.
As described above, the optical axis of the laser beam 2 emitted from the semiconductor laser 1 is substantially aligned with that of the optical system. That is why the center 111C of the far-field pattern 111 agrees with the center 112C of the aperture area 112 of the condenser lens 7 in the x direction. On the other hand, the optical axis of the laser beam 14 emitted from the semiconductor laser 13 is offset with respect to that of the optical system. Therefore, the center 201C of the far-field pattern 201 of the laser beam 14 emitted from the semiconductor laser 13 is offset with respect to the center 202C of the aperture area 202 of the condenser lens 7 in the x direction.
The gap Δ between the semiconductor lasers 1 and 13 is supposed to be 0.11 mm. The semiconductor lasers 1 and 13 are supposed to have an angle of radiation θx (Lo) of 8 degrees in the x (horizontal) direction in its low output mode and an angle of radiation θx (Hi) of 10 degrees in the x (horizontal) direction in its high output mode. Meanwhile, the angle of radiation θy thereof in the y (vertical) direction is supposed to be constant at 17 degrees without depending on the output. The collimator lens 3 is supposed to have a focal length fc of 20 mm. The condenser lens 7 is supposed to have a circular aperture. The aperture area 112 defined by the laser beam 2 emitted from the semiconductor laser 1 is supposed to have a radius rA1 of 2 mm, while the aperture area 202 defined by the laser beam 14 emitted from the semiconductor laser 13 is supposed to have a radius rA2 of 1.5 mm. The detector 5 is supposed to have a circular photosensitive area. The photosensitive areas 113 and 203 defined by the laser beams 2 and 14 emitted from the semiconductor lasers 1 and 13, respectively, are supposed to have a radius rA1 of 0.35 mm.
Suppose the intensity of the light emitted from the semiconductor laser 1, transmitted through the condenser lens 7 and then incident on the storage medium 8 is identified by Po1; the intensity of the light emitted from the semiconductor laser 1 and then incident on the optical power monitoring detector 5 is identified by Pm1; the intensity of the light emitted from the semiconductor laser 13, transmitted through the condenser lens 7 and then incident on the storage medium 8 is identified by Po2; and the intensity of the light emitted from the semiconductor laser 13 and then incident on the optical power monitoring detector 5 is identified by Pm2. Then, to minimize the variation in Pm1/Po1 ratio with Δθx (i.e., the variation in θx with the optical power), the distance dBx1 from the center 111C of the far-field pattern 111 of the light emitted from the semiconductor laser 1 to the center 113C of the photosensitive area 113 in the x direction is preferably 0.87.
In this case, the semiconductor laser 13 is arranged such that its emission point and the center 203C of the photosensitive area 203 are located on the opposite sides of the optical axis of the optical system in the x direction as shown in
In this case, the dependences of Po and Pm on Δθx are represented by the curves 211-a and 212-a, respectively, as shown in
On the other hand, if the detector 5 is arranged such that its photosensitive area 113 and the emission point of the semiconductor laser 13 are located on the same side of the optical axis of the optical system (i.e., if dB1x=−0.87 mm), then the variation in Pm1/Po1 ratio with Δθx can also be reduced as well as the situation where dB1x=0.87 mm. In that case, however, the difference in Δθx dependence between Po2 and Pm2 increases as represented by the curves 211-b and 212-b in
That is to say, to reduce the variation in Pm1/Po1 with Δθx of the semiconductor laser 1, the center 113C of the photosensitive area 113 of the detector 5 may be offset in either +x direction or −x direction because the same effects are achieved in either case. However, to reduce the variation in Pm2/Po2 with Δθx of the semiconductor laser 13 that is arranged in parallel with the semiconductor laser 1 in the x direction, the detector 5 is preferably arranged such that the offset of the center 113C of the photosensitive area 113 of the detector 5 satisfies dB1x>dB2x when rA1>rA2. Then, the Pm1/Po1 variation and the Pm2/Po2 variation can be both reduced sufficiently. In the same way, when rA1<rA2, the detector 5 is preferably arranged such that the offset of the center 113C of the photosensitive area 113 of the detector 5 satisfies dB1x<dB2x. Then, the Pm1/Po1 variation and the Pm2/Po2 variation can be both reduced sufficiently. By using light sources that emit light beams with mutually different wavelengths, the detector 5 may have photosensitive areas of different sizes. That is why these conditions are preferably standardized by the sizes of the photosensitive areas for the respective light sources. Specifically, if (rA1/rB1)>(rA2/rB2), then (dB1x/rB1)>(dB2x/rB2) is preferably satisfied. On the other hand, if (rA1/rB1)<(rA2/rB2), then (dB1x/rB1)<(dB2x/rB2) is preferably satisfied.
The conditions for reducing the variation in Pm/Po with the angle of radiation of the light source to ±6% or less are the same as those already described for first preferred embodiment. That is to say, rA1x, rB1x, dA1x and dB1x preferably satisfy the inequalities dA1x<0.25 rA1x and 0.25 rA1x<dB1x<0.55 rA1x.
Also, as already described for the first preferred embodiment, the center of the photosensitive area of the detector 5 may be offset arbitrarily in the y direction. Accordingly, by offsetting the center of the photosensitive area of the optical power monitoring detector with respect to the center of the far-field pattern defined by the light emitted from the semiconductor laser and to the center of the aperture area of the condenser lens in the y direction, the Pm1/Po1 variation and Pm2/Po2 variation can be both reduced and the intensities of the light beams entering the optical power monitoring detector can be equalized with each other, too.
Furthermore, the optical power monitoring detector may also be shifted in the y direction such that the photosensitive area of the detector is located outside of the aperture area of the condenser lens and outside of the reflective mirror. Then, the light can be guided to the condenser lens without sacrificing the intensity of the light for the purpose of monitoring the optical power.
Various preferred embodiments of the present invention described above can be used effectively in an optical information processor for at least one of reading and writing information optically, and are applicable particularly effectively to an optical information processor such as an optical disk drive including one, two or more light sources, of which the angle of radiation changes with the optical power.
This application is based on Japanese Patent Applications No. 2004-332991 filed on Nov. 17, 2004 and No. 2005-327272 filed Nov. 11, 2005, the entire contents of which are hereby incorporated by reference.
While the present invention has been described with respect to preferred embodiments thereof, it will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than those specifically described above. Accordingly, it is intended by the appended claims to cover all modifications of the invention that fall within the true spirit and scope of the invention.
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